1. Field of the Invention
The optical inspection apparatus incorporates two primary components, i.e., an explosion-proof light projector and a viewing periscope. The optical inspection apparatus is intended for use in an explosive environment including but not limited to natural gas pipelines and metering stations connected to natural gas pipelines. The invention could also be used in any other explosive environment such as the interior of tanks or vessels containing petrochemicals or other explosive fluids for non-destructive inspection thereof. This invention is not intended to be used as a medical instrument for the examination of humans or animals.
One embodiment of this invention must be connected to an external power source, 110 VAC current. An alternative embodiment is powered by batteries protectively enclosed within an explosion-proof housing. This alternative embodiment is portable and can be used in remote locations where conventional external power sources are unavailable or in other locations where portable AC generators are contraindicated or not readily available. Both embodiments are specially constructed for use in an explosive environment although they would also be equally operable in a nonexplosive environment.
2. Description of the Prior Art
Various efforts have been made to develop portable explosion-proof optical inspection devices including, but not limited to, U.S. Pat. application Ser. No. 771,349 filed on Aug. 30, 1985, by Robert H. Welker and now U.S. Pat. No. 4,678,290. The present invention presents several advantages not found in the aforementioned patent application. In the prior application, a light bulb is mounted in a reflector inside the periscope. Light from the bulb is reflected by a mirror through an aperture to the exterior of the periscope. The periscope of the prior application is typically inserted into an explosive environment such as a natural gas pipeline. The light bulb itself and the electrical connection with the wires is blanketed in a nitrogen atmosphere to prevent an explosion in the event of a spark. As a further precaution, the light bulb and reflector assembly is further isolated from the explosive environment by a clear lens.
The present invention does not insert a light bulb in to the explosive environment, nor are any wires carrying electricity immersed in the gas stream inside a pipeline. Therefore, the present invention is capable of using a much brighter light bulb, 150 watts, than the 18 watt bulb typical of the apparatus of the invention disclosed in the aforementioned application. A brighter light source allows inspection at greater distances from the periscope. A brighter light source is particularly advantageous when examining the interior of non-illuminated cavities which are often coated with dark irregular deposits such as those accumulations frequently found on the interior of meter tubes.
The apparatus of the prior application has a nominal outside diameter of one inch and is therefore capable of being inserted into a one inch NPT fitting or coupling having a nominal inside diameter of 1 5/32 inches. Unfortunately there are more 1/2 inch NPT fittings available in actual field situations than 1 inch NPT fittings. Both the viewing periscope and the light probe of the preferred embodiment of this invention have a nominal outside diameter of 11/16 inches which can be inserted into a 1/2 inch NPT fitting which has a nominal inside diameter of 23/32 inches. The apparatus of the present invention has a smaller diameter than the preferred embodiment of the prior application and therefore has a much greater range of practical application because of the greater availability of 1/2 inch NPT fittings in actual field situations.
The present embodiment is smaller in diameter and yet has a brighter light than the apparatus disclosed in the prior application. These advantages are particularly relevant when many of the fittings currently in field use are 1/2 inch NPT. It should be obvious from the foregoing discussion that devices with unusually large diameters such as two inches could project brighter lights than the present invention and the prior application. However there are very few two inch fittings in meter tubes or any other field application. The present application is therefore a strategic compromise between brilliance and size. The present application is believed to have the brightest light for its size of any apparatus developed to date which is battery powered and explosion-proof.
Various other types of primitive inspection devices have been known in the art for at least 50 years. U.S. Pat. No. 2,028,430 discloses an oil tank inspection device contained within an elongate tube housing both a light source and a mirror for examination of the interior of said tank. U.S. Pat. No. 2,437,458 discloses an inspection periscope including a light source and mirror for visual inspection of drums or pipes. Both of these devices are not suitable for explosive environments.
More modern devices such as the endoscope disclosed in U.S. Pat. No. 3,297,022 rely upon fiberoptic light guides for light transmission. Such devices are well suited in medical applications for examining objects no more than a few inches from the tip of the endoscope. However, the amount of light capable of being transmitted through the medical instrument disclosed in U.S. Pat. No. 3,297,022 is insufficient for industrial applications. In medical applications, the object to be observed is often less than an inch away from the light source. In industrial applications, the object to be observed will often be several feet or several yards from the light source. Light intensity, therefore, is critical in industrial applications where the object to be examined is far removed from the light source.
The length of a meter station will increase with the size of the pipeline. For example, a two inch diameter pipeline will typically have a meter tube length of approximately 20 feet; an 18 inch diameter pipeline will typically have a meter tube length of approximately 60 feet. Additional connective piping including a spool will further increase the length of the meter station. Such great lengths suggest increased light intensities.
The present invention discloses a brilliant light source contained in an explosion-proof housing which is capable of illuminating the entire distance of a typical meter station up to 60 feet in length; these features are not disclosed in the prior art. Other U.S. patents disclosing various types of optical inspection devices are disclosed in the information disclosure statement filed herewith.
Olympus Corporation apparently manufactures a portable explosion-proof illuminator which is listed with Underwriters Laboratories. The Olympus AXL-100 Explosion-Proof Light Source is not battery powered. The Olympus device must be plugged into an external energy source. One embodiment of the present invention discloses an explosion-proof light projector which is powered by self-contained batteries, which is highly portable and can be taken to any remote location. The Olympus illuminator must be connected to a fiberoptic light guide to function as a light projector such as that disclosed herein.
Lennox Instruments advertises an explosion-proof borescope light source, which also requires a remote power supply.
Other types of borescopes and various industrial inspection devices are also disclosed in the Information Disclosure Statement filed herewith.
The goal for one embodiment of the present invention is to provide a portable battery powered explosion-proof optical inspection device which possesses the following characteristics: First, the intensity of light must be bright enough to conduct a thorough inspection up to 60 feet away from the probe under adverse conditions such as a highly contaminated non reflective meter tube or pipeline. Second, the device should be able to operate at sustained brilliance for 25 to 30 minutes on one charge of the battery. Third, the device must not thermally damage the recharging capability of the batteries. Fourth, the device should be small enough to fit into a 1/2 inch NPT fitting. Combining all of these characteristics in a portable explosion-proof apparatus is a significant advance in the art.
Time of operation on one battery charge is important for practical field applications. It is estimated that during one day of field inspection of meter tubes the optical inspection device will only be in operation for approximately 25 to 30 minutes. The remainder of the day will be spent driving from one meter station to another in which case the optical inspection device will not be in use. Other activities such as cleaning dirty tubes will occupy the remainder of a typical day. At the end of the day, the device can be returned to the shop and fully recharged. From a practical perspective the optical inspection device must have sufficient energy to function at a sustained level during a typical day of use by field personnel; 25-30 minutes of operating capacity normally suffices.